Generally, packings are used as seal members in the gland portion of a regulating valve (see, for example, PTL 1). Of these packings above, a V-packing or a yarn packing is known as a main packing for primarily preventing a fluid from leaking from the inside of the valve box of a regulating valve.
As illustrated in FIGS. 9 and 10, a yarn packing is widely used as a main packing for a regulating valve since it has higher seal performance for a mechanical cycle, such as the reciprocating motion of a valve stem, than a V-packing. For example, in the case of a regulating valve used in an application for controlling a fluid as the control target at a temperature of 230 degrees or less, a yarn packing made of a fluororesin (for example, Teflon® (registered trademark, this is the same in the following)) is used as a main packing.